Lash in a vehicle may occur due to lost motion caused by slack or clearance within components of a vehicle driveline. Driveline torque transitions through zero torque during powertrain braking or propulsion may create clunk or backlash in the driveline causing driver discomfort. By gently taking up lash before substantial torque is applied, effects of crossing the lash zone may be mitigated to reduce driver discomfort and improve vehicle drivability. Several approaches of managing lash in a vehicle transmission system have been studied.
On example approach of managing driveline lash is provided by Yamazaki et al. in U.S. Pat. No. 8,954,215. Therein, a controller controls torque from a traction motor coupled to an engine and driveline input torque to vehicle wheels during torque reversal from positive to negative torque in order to limit the rate of change of traction and driveline torque. In another example, shown by Stroh in U.S. Pat. No. 7,171,299, a rate of torque change in a vehicle driveline may be reduced to threshold levels by a system with a torque based module, a filter and an engine control module. The torque based module generates a torque request based on operator input. The filter, whose parameters are determined based on engine operating conditions, modifies the torque request by reducing torque changes to a predetermined torque range. The engine control module receives the modified torque request and controls engine throttle and spark timing to improve engine efficiency and minimize emissions.
However, the inventors herein have recognized potential issues relating to such methods of managing lash in a vehicle driveline. Specifically, lack of lead information on a driver intent (such as whether the driver will eventually brake or accelerate) to guide adjustments in driveline torque may create slow vehicle response and reduce vehicle drivability. For example, a driveline torque may be adjusted during an accelerator pedal tip-out assuming that the operator is going to apply the brake pedal. However, if the operator does not apply the brake pedal but coasts and then reapplies the accelerator pedal, then the driveline torque may unnecessarily transition through the lash zone multiple times. As a result, repeated lash adjustments may slow down vehicle response and also create additional driver discomfort.
Thus in one example, some of these issues may be at least partly addressed by a method for a vehicle engine, comprising: in response to an operator foot-off pedal event, distinguishing between a driver intent to brake or coast based on one or more of operator foot motion inside the vehicle and traffic patterns outside the vehicle; and varying lash adjustments during torque transition through a lash region following the operator foot-off accelerator pedal event based on the driver intent. In this way, torque adjustments may be selected that better manage movement through a lash region based on an upcoming torque transition.
As one example, responsive to a foot-off accelerator pedal event, a controller may initiate powertrain braking to reduce torque. In addition, the controller may infer and distinguish a driver intent to brake from a driver intent to coast based on the output of a camera inside a vehicle foot-well area, the output from a traffic sensor, operator drive history, etc. Based on the inferred driver intent, lash adjustments for the driveline may be varied. For example, based on a driver foot motion towards a brake pedal and/or in response to significant traffic ahead of the vehicle following the foot-off accelerator pedal event, the controller may infer that the driver is likely to brake and may adjust the lash in the vehicle driveline by providing a slight negative torque (since substantial negative torque is expected thereafter during the braking event). In addition, the controller may initiate a transition through the lash region to a creep torque later. As another example, based on driver foot remaining near the accelerator brake pedal and/or traffic clearing in front of the vehicle following the accelerator foot-off pedal event, the controller may infer that the driver is likely to coast and may maintain a slight positive torque in the driveline (since substantial positive torque is expected thereafter during the coasting event) and may not transition through the lash region unless the operator applies the brake pedal. Alternatively, the controller may initiate a transition through the lash region to a creep torque earlier.
The approach described here may confer several advantages. For example, the method allows driveline torque adjustments to be made in a timely manner to improve vehicle response and improve drivability. By using output from the foot camera and traffic sensor to determine if the operator intends to brake or coast, the expected torque profile following a foot-off pedal event may be better predicted, allowing for lash adjustments to be accordingly performed. By adjusting the amount and rate of powertrain braking torque applied following the foot-off pedal event based on the predicted torque profile, torque transitions through the lash zone may be conducted with improved efficiency. By maintaining a slight positive torque in the driveline when the driver is anticipated to coast, frequent transitions through the lash region are reduced, providing fuel economy and NVH benefits. Consequently, vehicle response during lash adjustments may be improved, improving vehicle drivability, and minimizing torque variations. By improving lash adjustments, driveline component life may be extended.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.